Cleaning the tip with povidone-iodine solution significantly reduces power output from a radial emission endovenous laser catheter using 1470 nm

Abstract

Background

Endovenous laser ablation (EVLA) is a first line recommended treatment for incompetent truncal veins in the legs. The current “industry standard” is a single ring radially firing catheter, using a 1470 nm diode laser. It is common for doctors to treat more than one vein, and they often clean the catheter tip before re-introduction. We have observed some doctors using normal saline for this, but others using povidone-iodine. The aim of this in vitro study was to determine whether povidone-iodine reduces the power being emitted from the catheter tip.

Methods

Five radial catheters were tested, each connected in turn to a 1470 nm diode laser set at 10 W. Power emission was measured by a laser power detector connected to a power meter. The power meter recorded an average (mode) of the readings once the laser had reached a steady state. Each catheter was tested firing in air, after dipping in normal saline, then povidone-iodine and finally after wiping the povidone-iodine off the tip with a surgical gauze.

Results

The emitted power recorded for air (9.05 W) was significantly (p < .05) more than for normal saline (8.90 W), povidone-iodine (8.69 W) and post-wiping off povidone-iodine (8.87 W). The power emitted with povidone-iodine on the tip was significantly less than with normal saline, which mimics the situation of the catheter in a vein surrounded by tumescence anaesthesia.

Conclusion

In a laboratory setting, povidone-iodine on the tip of a radially firing catheter transmitting laser energy at 1470 nm, significantly reduces the power being emitted. As this was a laboratory-based study, clinical studies are required to see if this translates into a significant problem during EVLA treatment.

Keywords

EVLA LEED power povidone-iodine normal saline

Introduction

Endovenous laser ablation (EVLA) is a catheter-based technique for endovenous thermal ablation of incompetent truncal veins in the lower limb. It is one of the first line techniques recommended in international guidelines for treating varicose veins.^1–3 Radially emitting catheters have become popular due to the laser energy being directed at the vein wall, the target for the ablation.⁴ However, in order to get the laser energy to be emitted radially from the end of the laser fibre, a clear plastic tip is required. This tip holds an air-bubble next to the shaped end of the optical fibre, to ensure the correct refraction of energy from the fibre.⁵

It is not uncommon for patients to require EVLA of multiple venous trunks in the same session.⁶ During such multi-trunk procedures, it is common for the endovenous laser catheter to develop a layer of carbonised tissue on its tip. There is naturally a concern that this layer of carbonised tissue might interfere with the transmission of the laser energy to the vein wall. In addition, this build-up causes the catheter to stick to the vein wall during pull-back. Hence it is usual practice for practitioners to clean the fibre tip between insertions into the veins.

During the cleaning process, we have observed that practitioners often use normal saline, or povidone-iodine solutions. However, there is no data available to show whether there is an impact of different cleaning agents on the power output of the laser fibre.

We performed this trial to investigate whether cleaning an EVLA radial catheter tip with normal saline or povidone-iodine has any impact on the power being delivered at the laser catheter tip.

Methods

This study was performed in a laboratory. Each radial laser catheter (600 µm radial emission fibre, Oberon Gmbh, Wildau, Germany) was connected to a diode laser console that emitted laser energy with a wavelength of 1470 nm (Vari-lase®, Vascular Solutions Inc., Minneapolis, Minnesota, USA) Figure 1. The fibre was then positioned to fire perpendicularly onto a laser power detector (Edmund Optics® Europe, York, UK), Figure 2, which was connected to a power meter (EO Premier Power/Energy Meter, Edmund Optics, York, UK) Figure 3. This power meter was set to record the power 10 times per second, and to display the results on the screen as well as record all readings digitally onto a USB for analysis. This analysis was performed by downloading the digital information into Excel (Version 2407 – Build 17,830.20210 – Microsoft, USA).

Figure 1.

Varilase® 1470 nm diode laser console.

Figure 2.

Radial laser fibre being held in position for the emitted laser energy to be incident on the laser detector. The fibre is held in place by surrounding it with gauze, which is held in position by a laboratory clamp.

Figure 3.

The power meter used to record the power being measured at the detector.

The laser console was set to 10 W and laser safety regulations were observed. Initially each catheter was fired at the detector until the power meter recorded a steady power.

The catheter tip was then dipped into 0.9% normal saline, and the process repeated. Once a steady power was reached the laser was switched off and the tip dried. The laser was then fired again to ensure that the original power had been restored in case heating of the normal saline had made any permanent effect on the tip.

The catheter tip was then dipped into povidone-iodine (Videne®, containing 10% povidone-iodine, Ecolab Ltd, Caerphilly, UK) and then the laser was fired at the detector again until a steady power was reached. Finally, the povidone-iodine was wiped off with a surgical gauze swab and the laser was fired one final time.

This process was repeated for five endovenous catheters to ensure reproducibility and to account for any variability between catheters. For each set of readings, the average (mode) of the readings was recorded, when the power had reached a steady state.

Statistical analysis was performed using a t test calculator for two dependent means (https://www.socscistatistics.com/tests/ttestdependent/default.aspx) with p < .05 being regarded as statistically significant. As a laboratory study with no subjects, ethical approval and clinical trial registration were not required.

Results

As we have reported previously, the recorded power being emitted from the tip of the laser catheter is less than the power indicated on the laser console, due in part to power losses between diode and catheter tip.⁷ Hence despite the laser being set to 10 W, the average (mode) power recorded was 9.05 W (Table 1).

Table 1.

The average (mode) power for each of 5 catheters being fired at the detector in air, after dipping in normal saline, povidone-iodine and then having the povidone-iodine wiped off with a surgical gauze.

Catheter	Average (mode) of power readings when in steady state with console set at 10 W (W)
Catheter	Air	N/Saline	Povidone-iodine	Post povidone-iodine
1	8.80	8.56	8.43	8.74
2	9.07	9.01	8.84	8.89
3	8.78	8.75	8.16	8.53
4	9.35	9.17	9.13	8.99
5	9.25	9.02	8.90	9.19
Average (mean)	9.05	8.90	8.69	8.87

Values in bold are the average (mean) of the values listed for the 5 catheters.

When the tip was dipped into normal saline before the laser was fired, there was a reduction in the recorded power being emitted from the tip, with an average (mode) power of 8.90 W. This reduction in power was statistically significant at p < .05 (Table 2).

Table 2.

Comparison of the results of the average (mode) powers for each of the combinations in Table 1.

Results being compared	Comparison of average (mode) powers (W)	Statistical significance
Air v N/Saline	9.05 v 8.90	p < .05 - significant
Air v povidone-iodine	9.05 v 8.69	p < .05 - significant
Air v post povidone-iodine	9.05 v 8.87	p < .05 - significant
N/Saline v povidone-iodine	8.90 v 8.69	p < .05 - significant
N/Saline v post povidone-iodine	8.90 v 8.87	p > .05 – Not significant
Povidone-iodine v post povidone-iodine	8.69 v 8.87	p > .05 – Not significant

Values in bold are those showing a statisitcally significant difference at the p < .05 level.

The tip was dried with a cotton surgical gauze and the power re-tested to ensure that the initial output had been restored. This is not reported in Table 1 as in all cases, the power returned to the original power output in air.

The tip was then dipped into the povidone-iodine and the laser fired at the power meter detector again. This showed a decrease in emitted power, with an average (mode) of 8.69 W, which was significantly lower than the power recorded both when the laser tip was dry and in air, and when it had been dipped in normal saline (Table 2).

Finally, the povidone-iodine was wiped off the catheter tip using a cotton surgical gauze and the power output tested one last time. This was done to see if the residual iodine staining that can be seen as a slight brown discolouration of the catheter tip that was present after wiping the povidone-iodine, has any adverse effect on the power emission. It transpired that this residual povidone-iodine staining did reduce the power emission from the catheter tip to an average (mode) of 8.87 W.

Discussion

Doctors performing EVLA rely upon the power being displayed on the laser console to be an accurate reflection of the energy being emitted from the tip of the EVLA catheter during treatment. It is this displayed power that is used to calculate the Linear Endovenous Energy Density (LEED).⁸ The LEED is the measurement used to determine the dose of laser energy used to ablate the target vein.^9,10

Interestingly, as the measured power is about 10% less than the power displayed on the console, there is a difference between the LEED measured by doctors and written in the notes and in research papers, and the actual LEED that the target veins receive. For example, if the console displays 10 W, and the pull-back is 7 sec/cm, the recorded LEED is 70 J/cm. However, using the output power measured from the tip in this paper of 9.05 W, the actual LEED is 63.35 J/cm, 9.5% lower than that recorded by the doctor.

Furthermore, as the laser catheter is surrounded by tumescence anaesthesia when in use, the actual power output during a procedure is more likely to be that which we have measured with normal saline on the tip – that is: 8.90 W (Table 2). Thus, with a 7 sec/cm pull-back, the actual LEED being absorbed by the target vein during the treatment is 8.90 W × 7 sec/cm = 62.3 J/cm, which is only 89% of the recorded LEED of 70 J.cm.

However, it could be argued that this probably doesn’t matter provided the doctor understands this discrepancy and uses the same laser console and fibre supplier for all their cases. As such, they will get used to their own outcomes, and hence the LEED recorded in the patient notes can be used as a comparative guide, rather than an absolute measurement of energy used.

As such, anything that further reduces the power being emitted from the laser catheter tip increases the discrepancy between the recorded LEED and the actual LEED.

We have found that povidone-iodine on the catheter tip reduces the power output to 8.69 W. Hence using the above example, if povidone-iodine is used to clean the catheter tip, the actual LEED would be 60.83 J/cm, an 87% reduction from the 70 J/cm calculated from console energy and pull-back. Even if the povidone-iodine is wiped off with a cotton surgical gauze, the actual LEED would be 8.87 W × 7 sec/cm = 62.09 J/cm, 88.7% of the recorded LEED.

There are clearly limitations in this laboratory-based study as we are only looking at one variable affecting the energy emission from the catheter tip. Of course, in the clinical setting, there are many other variables that would influence any real variations in energy output from the tip of the laser catheter. For instance, we don’t know if aggressive cleaning in cases where carbonised tissue has accumulated on the tip might damage the surface of the clear plastic end, which might enhance the power loss due to more povidone-iodine being retained. Furthermore, we don’t know the cumulative effects of cleaning the tip with povidone-iodine and then firing the laser with the catheter inside the vein for multiple veins.

In addition, we have only tested one type of radial catheter and only tested the effects when using a wavelength of 1470 nm. Furthermore, we only tested the emission at 10 W as reported on the laser console, and didn’t test the effect at other powers.

In conclusion, we have shown that in a laboratory setting, the use of povidone-iodine to clean the tip of a radially firing catheter tip, reduces the power being emitted when the 1470 nm laser is being fired. As this was a laboratory-based study, clinical studies are required to see if this translates into a significant problem during EVLA treatment.

Footnotes

Author contributions

Conception or design of the work AL

Data collection AL, MSW

Data analysis and interpretation MSW

Drafting the article AL

Critical revision of the article MSW

Final approval of the version to be published AL, MSW

Declaration of conflicting interests

The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

The author(s) received no financial support for the research, authorship, and/or publication of this article.

Guarantor

Prof. Mark S Whiteley

ORCID iDs

Alex Lapenga

Mark S Whiteley

References

NICE (National Institute for Health and Care Excellence) clinical guidelines - CG 168 . Varicose veins in the legs: the diagnosis and management of varicose veins. Issued, 2013.

Wittens

Davies

Baekgaard

, et al. Editors choice – management of chronic venous disease: practive guidelines of the European society for vascular surgery. Eur J Vasc Endovasc Surg 2015; 49: 678–737.

Gloviczki

Comerota

Dalsing

, et al. The care of patients with varicose veins and associated chronic venous diseases: clinical practice guidelines of the society for vascular surgery and the American Venous Forum. J Vasc Surg 2011; 53(5): 2S–48S.

Bontinis

Giannopoulos

, et al. Endovenous laser ablation (EVLA) 980 nm versus 1470 nm and the impact of fiber type: a systematic review and meta-analysis. Laser Med Sci 2024; 39(1): 165.

Hirokawa

Kurihara

. Comparison of bare-tip and radial fiber in endovenous laser ablation with 1470 nm diode laser. Ann Vasc Dis 2014; 7(3): 239–245.

Verbist

Laeremans

Gryffroy

, et al. Durability and efficacy of the ELVeS® Radial® 2ring slim fiber for multiple ablations. Phlebology 2023; 38(10): 641–648.

Davies

Riley

Dabbs

, et al. Comparison of laser power output from the fiber tip during endovenous laser ablation against displayed power and the “first treatment” effect. J Vasc Surg Venous Lymphat Disord 2021; 9(4): 1051–1056.

Proebstle

Moehler

Gül

, et al. Endovenous treatment of the great saphenous vein using a 1,320 nm Nd:YAG laser causes fewer side effects than using a 940 nm diode laser. Dermatol Surg 2005; 31(12): 1678–1683.

Bontinis

Giannopoulos

, et al. Mid-term and long-term outcomes of endovenous laser ablation utilizing a 1470 nm laser a systematic review and meta-analysis. J Endovasc Ther 2024; 0: 15266028241305955.

10.

Borsuk

Fokin

Lobastov

, et al. A randomized clinical trial to assess the impact of laser power with constant linear endovenous energy density on outcomes of endovenous laser ablation (SLEDGE trial). J Vasc Surg Venous Lymphat Disord 2023; 11(5): 946–953.